JP6757504B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in portable terminals, electric vehicles, hybrid vehicles, etc., and are expected to continue to improve energy density in the future. Currently, the positive electrode active material of lithium ion secondary batteries currently in practical use is lithium transition metal oxide, the negative electrode active material is carbon material, and the electrolyte is mainly a non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous solvent. It is used in.

Studies are underway to use sulfur as a positive electrode active material for non-aqueous electrolyte secondary batteries as a substitute for lithium transition metal oxides. Since sulfur has a large theoretical capacity of 1675 mAh / g per mass, it is expected as a next-generation positive electrode active material for increasing the capacity.
However, a shuttle in which self-discharge proceeds by elution of lithium polysulfide (Li _{2 Sn} , 4 ≦ n ≦ 8) generated at the positive electrode during charging / discharging into a non-aqueous electrolyte, reaching the negative electrode and reducing the amount. The phenomenon has become an issue. A technique of arranging a cation exchange resin layer between a positive electrode and a negative electrode is known in order to suppress the shuttle phenomenon. (Patent Documents 1 to 3 and Non-Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2015-128063 International Publication No. 2015/0833114 Japanese Patent Application Laid-Open No. 2015-507738

Journal of Power Sources, Vol. 251 p. 417-422 (2014) Journal of Power Sources, Vol. 218, p. 163-167 (2012)

When a cation exchange resin layer is provided between the positive electrode and the negative electrode, the resistance at the interface between the positive electrode and the cation exchange resin layer or the negative electrode and the cation exchange resin layer is large, and the non-aqueous electrolyte secondary battery has the cation exchange resin layer. The present inventors have found a problem that the high rate discharge performance of the above is low.

The non-aqueous electrolyte secondary battery according to one aspect of the present invention for solving the above problems is arranged between a positive electrode containing sulfur, a negative electrode, a non-aqueous electrolyte, and a positive electrode and a negative electrode, and has a roughness factor of 3. The cation exchange resin layer having the above-mentioned first surface is provided.

According to one aspect of the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having a low interfacial resistance on the first surface of the cation exchange resin layer and having excellent high rate discharge performance.

It is external perspective view of the non-aqueous electrolyte secondary battery which concerns on 1st Embodiment. It is a schematic cross-sectional view which shows the local structure of the non-aqueous electrolyte secondary battery of this embodiment. It is a schematic diagram which shows the power storage device which was configured by gathering a plurality of non-aqueous electrolyte secondary batteries which concerns on 1st Embodiment. It is a schematic cross-sectional view which shows the structure of the cell for resistance measurement used in the Example of this Embodiment. It is a schematic cross-sectional view which shows the structure of the test cell used in the Example of this Embodiment. It is a figure which shows the relationship between the interfacial resistance and the roughness factor of the surface of a cation exchange resin layer in an Example. It is a figure which shows the relationship between the interfacial resistance and the arithmetic mean roughness of the surface of a cation exchange resin layer in an Example. It is a figure which shows the relationship between the interfacial resistance and the maximum height roughness of the surface of a cation exchange resin layer in an Example. (A) It is a figure which shows the discharge curve of the Example battery 2-1 and (b) is a figure which shows the discharge curve of the comparative example battery 2-1.

The non-aqueous electrolyte secondary battery according to one aspect of the present invention is arranged between a positive electrode containing sulfur, a negative electrode, a non-aqueous electrolyte, and a positive electrode and a negative electrode, and has a first surface having a roughness factor of 3 or more. It is provided with a cation exchange resin layer having.

By having the above structure, the interfacial resistance of the first surface of the cation exchange resin layer is reduced, and the high rate discharge performance of the non-aqueous electrolyte secondary battery is improved.

The arithmetic average roughness Ra of the first surface of the cation exchange resin layer is preferably 0.5 μm or more.

When the arithmetic average roughness Ra of the first surface of the cation exchange resin layer is 0.5 μm or more, the interfacial resistance can be reduced.

The maximum height roughness Rz of the first surface of the cation exchange resin layer is preferably 5 μm or more.

Since the maximum height roughness Rz of the first surface of the cation exchange resin layer is 5 μm or more, the interfacial resistance of the first surface of the cation exchange resin layer can be reduced even when the electrolyte salt concentration is low.

The non-aqueous electrolyte secondary battery may further include a porous layer. In that case, the porous layer is preferably in contact with the first surface of the cation exchange resin layer.

As will be described in detail later, in the cation exchange resin layer, the cations move selectively (preferentially), and the movement of anions is unlikely to occur. On the other hand, both the cation and the anion can move in the porous layer impregnated with the non-aqueous electrolyte containing the cation and the anion. Therefore, in a non-aqueous electrolyte secondary battery provided with a cation exchange resin layer and a porous layer, the resistance at the interface between the cation exchange resin layer and the porous layer tends to be large because the ion transfer mechanism is different. .. As described above, by applying the present embodiment to the non-aqueous electrolyte secondary battery having high interfacial resistance, the interfacial resistance is remarkably reduced, and a non-aqueous electrolyte secondary battery having excellent high rate discharge performance can be obtained. Can be done.

The non-aqueous electrolyte comprises a positive electrode electrolyte disposed between the positive electrode and the cation exchange resin layer, and a negative electrode electrolyte disposed between the negative electrode and the cation exchange resin layer, and the positive electrode electrolyte contains lithium polysulfide. It is preferable that the sulfur equivalent concentration of the negative electrode electrolyte is lower than the sulfur equivalent concentration of the positive electrode electrolyte.

With the above configuration, a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance can be obtained.

In the above configuration, the sulfur equivalent concentration of the positive electrode electrolyte is preferably 1.2 mol / l or more.

With such a configuration, not only the charge / discharge cycle performance can be improved, but also the charge / discharge efficiency after the cycle can be increased.

In the above configuration, the sulfur equivalent concentration of the positive electrode electrolyte is preferably 3.0 mol / l or more.

With such a configuration, a non-aqueous electrolyte secondary battery having a high capacity and a high energy density can be provided.

The sulfur equivalent concentration of the positive electrode electrolyte is preferably 18 mol / l or less.

With such a configuration, the viscosity of the positive electrode electrolyte does not increase too much, and the interfacial resistance between the positive electrode electrolyte and the cation exchange resin layer does not become too high. Therefore, the sulfur utilization rate is high and the energy density of the non-aqueous electrolyte secondary battery is high. Is obtained.

In the above configuration, the concentration of anions contained in at least one of the positive electrode electrolyte and the negative electrode electrolyte is preferably 0.7 mol / l or less.

With such a configuration, a non-aqueous electrolyte secondary battery having a low interfacial resistance between the non-aqueous electrolyte and the cation exchange resin layer can be obtained.

The concentration of the anion contained in the positive electrode electrolyte is preferably 0.3 mol / l or less.

With the above configuration, even if the concentration of lithium polysulfide contained in the positive electrode electrolyte is increased, the interfacial resistance between the non-aqueous electrolyte and the cation exchange resin layer does not easily increase, and the non-aqueous electrolyte secondary battery has a high capacity. be able to.

At least one of the positive electrode and the negative electrode may contain a cation exchange resin, and the concentration of anions contained in the non-aqueous electrolyte may be 0.7 mol / l or less.

With such a configuration, a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle performance can be obtained.

Hereinafter, the non-aqueous electrolyte secondary battery according to the embodiment of the present invention will be described. Each of the embodiments described below shows a preferred specific example of the present invention. Numerical values, shapes, materials, components, arrangement positions of components, connection forms, etc. shown in the following embodiments are examples, and are not intended to limit the present invention. Further, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept of the present invention will be described as arbitrary components constituting the more preferable form.

In the non-aqueous electrolyte secondary battery according to the present embodiment, the non-aqueous electrolyte secondary battery includes a positive electrode containing sulfur, a negative electrode, a cation exchange resin layer interposed between the positive electrode and the negative electrode, and between the positive electrode and the cation exchange resin layer. The positive electrode electrolyte (an example of a non-aqueous electrolyte) and the negative electrode electrolyte (an example of a non-aqueous electrolyte) arranged between the negative electrode and the cation exchange resin layer are provided, and the cation exchange resin layer has a roughness factor of 3 or more. It has the first side that is. The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery usually contains an electrolyte salt and a non-aqueous solvent, but in the present specification, the non-aqueous solvent containing no electrolyte salt is referred to as “non-aqueous electrolyte”. Sometimes. The roughness factor is the ratio of the actual surface area to the apparent unit surface area (geometric unit area), and is an index showing the roughness of the surface.

The cation exchange resin layer is a layer containing a cation exchange resin and has a role of a separator that keeps a positive electrode and a negative electrode in an insulated state. The cation exchange resin has a structure in which an anionic functional group such as a sulfonic acid group or a carboxylic acid group is bonded to a polymer mainly composed of a hydrocarbon. Due to the electrostatic interaction of this anionic group, it has high cation permeability, but low anion permeability. That is, the cation exchange resin allows lithium ions to pass through and is slightly dissociated in the positive electrode electrolyte (electrolyte solution) to prevent the passage of anionic lithium polysulfide. As a result, the cation exchange resin layer suppresses the movement of the lithium polysulfide from the positive electrode to the negative electrode, so that the shuttle phenomenon is suppressed.

In the cation exchange resin layer according to the present embodiment, the lower limit of the roughness factor of the first surface, which is at least one surface, is 3, preferably 4, and more preferably 10. The upper limit of the roughness factor of the first surface of the cation exchange resin layer is preferably 20, more preferably 18, and even more preferably 16. When the roughness factor is 3 or more, the resistance at the interface between the cation exchange resin layer and the non-aqueous electrolyte is reduced, so that the high rate discharge performance of the non-aqueous electrolyte secondary battery is improved.
The first surface of the cation exchange resin layer in the present embodiment has an arithmetic average roughness Ra defined in JIS B 0601: 2013, preferably 0.5 μm or more, more preferably 2 μm or more. When the arithmetic mean roughness Ra satisfies the above range, the resistance at the interface between the cation exchange resin layer and the positive electrode can be reduced. Further, in order to maintain the strength of the cation exchange resin layer, the arithmetic average roughness Ra is preferably 10 μm or less, more preferably 8 μm or less, still more preferably 5 μm or less.

The first surface of the cation exchange resin layer in the present embodiment preferably has a maximum height roughness Rz defined in JIS B 0601: 2013 of 5 μm or more, and more preferably 10 μm or more. When the maximum height roughness Rz satisfies the above range, the interfacial resistance can be reduced even when the electrolyte salt concentration in the non-aqueous electrolyte is low. The maximum height roughness Rz is preferably 30 μm or less, more preferably 28 μm or less.

The roughness factor, arithmetic mean roughness Ra, and maximum height roughness Rz of the first surface of the cation exchange resin layer are obtained by photographing and measuring the surface of the cation exchange resin layer under the following conditions and performing shape analysis.
-Measuring equipment: Ultra-depth shape measuring microscope VK-8500 (manufactured by KEYENCE)
-Measurement range: 1.04 x 10 ^-3 cm ²
-Shape analysis application: VK-H1A9 (manufactured by KEYENCE)

Examples of the roughening treatment method for setting the roughness factor of the surface of the cation exchange resin layer according to the present embodiment to 3 or more include a method of roughening the surface of the cation exchange resin layer with an abrasive such as sandpaper, and a sandblasting method. , Chemical etching method and the like. As the polishing material, it is preferable to use sandpaper having a particle size of the polishing agent for polishing padding specified in JIS R 6010: 2000 of 320 to 1000.

The thickness of the cation exchange resin layer according to the present embodiment is preferably 20 to 180 μm, more preferably 30 to 180 μm. When the thickness is 30 μm or more, the thickness of the cation exchange resin layer is sufficiently maintained even if the roughening treatment is performed, so that the handling at the time of battery production becomes easy. Further, by setting the thickness to 180 μm or less, the internal resistance of the battery can be reduced and the energy density of the battery can be improved.

The cation exchange resin layer may be formed by molding a mixture of the cation exchange resin and other polymers into a thin film and roughening the surface. As the other polymer, a material constituting the porous layer described later can be appropriately used.

The non-aqueous electrolyte secondary battery according to the present embodiment may further include a porous layer. The porous layer is preferably in contact with the first surface of the cation exchange resin layer.
Usually, the surfaces of the positive electrode and the negative electrode have irregularities derived from the particulate active material. Therefore, when a cation exchange resin layer having low flexibility is used, the contact area between the roughened first surface and the positive electrode or the negative electrode may be smaller than that in the case where the roughened first surface is not used. Since the porous layer containing the polymer is more flexible than the cation exchange resin layer, the positive electrode-porous layer-cation exchange occurs when the porous layer is in contact with the first surface of the cation exchange resin layer. Good contact between the first surfaces of the resin layer or between the negative electrode-porous layer-cation exchange resin layer first surface is maintained, and lithium ions are satisfactorily transferred. Further, since the non-aqueous electrolyte can be retained in the porous layer, uneven distribution of the non-aqueous electrolyte in the positive electrode or the negative electrode is unlikely to occur, and the charge / discharge reaction at the positive electrode or the negative electrode can be made uniform.
The porous layer may be provided only between the positive electrode and the first surface of the cation exchange resin layer, or may be provided only between the negative electrode and the first surface of the cation exchange resin layer. Alternatively, a porous layer may be provided both between the positive electrode and the cation exchange resin layer and between the negative electrode and the cation exchange resin layer.

In the present embodiment, the positive electrode electrolyte preferably contains lithium polysulfide. Further, it is preferable that the sulfur equivalent concentration of the positive electrode electrolyte is higher than the sulfur equivalent concentration of the negative electrode electrolyte. In the following description, the "positive electrode electrolyte" and the "negative electrode electrolyte" may be collectively referred to as a "non-aqueous electrolyte".

The cation exchange resin layer suppresses the movement of lithium polysulfide from the positive electrode to the negative electrode, but the lithium polysulfide produced at the positive electrode during the charge / discharge reaction is highly soluble in a non-aqueous solvent, so it is filled. Easily eluted into the positive electrode electrolyte during the discharge cycle. By mixing lithium polysulfide in advance with the positive electrode electrolyte arranged between the positive electrode and the cation exchange resin layer, the present inventors only suppress the elution of the lithium polysulfide generated at the positive electrode. Instead, it was found that the lithium polysulfide in the positive electrode electrolyte contributes to the charge / discharge reaction as the positive electrode active material, so that excellent charge / discharge cycle performance can be exhibited. That is, in the present embodiment, the positive electrode electrolyte contains lithium polysulfide, and the sulfur equivalent concentration of the positive electrode electrolyte is higher than the sulfur equivalent concentration of the negative electrode electrolyte, so that the non-aqueous electrolyte secondary battery having high charge / discharge cycle performance can be obtained. can get. Here, the sulfur-equivalent concentration is a value obtained by converting the concentration of the sulfur compound in the non-aqueous electrolyte into the concentration of the sulfur atom. That is, 1 mol / l lithium sulfide (Li ₂ S) corresponds to a sulfur equivalent concentration of 1 mol / l, and 1 mol / l Li ₂ S ₆ corresponds to a sulfur equivalent concentration of 6 mol / l, and 1 mol / l sulfur (S). ₈ ) corresponds to a sulfur equivalent concentration of 8 mol / l.

The lower limit of the sulfur equivalent concentration of the positive electrode electrolyte is preferably 1.2 mol / l, more preferably 1.5 mol / l, and even more preferably 3.0 mol / l. When the sulfur equivalent concentration is 1.2 mol / l or more, the charge / discharge efficiency after the charge / discharge cycle is improved. When the sulfur equivalent concentration is 3.0 mol / l or more, a non-aqueous electrolyte secondary battery having a high capacity and a high energy density can be realized.

The upper limit of the sulfur equivalent concentration of the positive electrode electrolyte is preferably 18 mol / l, more preferably 12 mol / l, and even more preferably 9 mol / l. When the sulfur conversion concentration is not more than the above upper limit, the viscosity of the positive electrode electrolyte does not increase too much, and the interfacial resistance between the positive electrode electrolyte and the cation exchange resin layer does not become too high, so that the sulfur utilization rate is high and the energy density is high. A non-aqueous electrolyte secondary battery can be obtained.

The lithium polysulfide contained in the positive electrode electrolyte is not particularly limited, but a lithium polysulfide represented by Li _{2 Sn} (4 ≦ n ≦ 8) is preferable.

The method for producing a lithium polysulfide represented by the composition formula Li _{2 Sn} (4 ≦ n ≦ 8) is not limited. For example, lithium sulfide (Li ₂ S) and sulfur (S ₈ ) at the desired composition ratio are mixed and stirred in a solvent, placed in a closed container, and reacted in a constant temperature bath at 80 ° C. for 4 days or more. By doing so, it can be obtained.

In the present embodiment, the negative electrode electrolyte preferably has a lower sulfur conversion concentration than the positive electrode electrolyte. That is, elemental sulfur contained in the negative electrode electrolyte, the sum of the concentration of the lithium polysulfide and Li 2 _S, is preferably lower than that of the positive electrode electrolyte. Lithium polysulfides, along with react with the negative electrode active material lowers the state of charge of the negative electrode active material, resulting in Li 2 _S as the reducing product. Since Li ₂ S is insoluble in a non-aqueous solvent, it precipitates on the surface of the negative electrode to reduce the reaction area of the negative electrode. Therefore, the upper limit of the sulfur-equivalent concentration of the negative electrode electrolyte is preferably 0.5 mol / l and may be 0 mol / l. Since it is known that lithium polysulfide reacts on the surface of the negative electrode to form a solid electrolyte coating (SEI), the negative electrode electrolyte preferably contains a small amount of lithium polysulfide.

In the non-aqueous electrolyte secondary battery according to the present embodiment, it is preferable that at least one of the positive electrode and the negative electrode is provided with a cation exchange resin. In this case, the concentration of the anion contained in the non-aqueous electrolyte is more preferably 0.7 mol / l or less.

The mode in which at least one of the positive electrode and the negative electrode is provided with the cation exchange resin is not particularly limited, but it is preferably provided on the surface or inside of the positive electrode mixture layer or the negative electrode mixture layer. That is, the cation exchange resin may cover the surface of the mixture layer, or may be present in at least a part of the inside of the mixture layer.

As described above, the cation exchange resin allows only cations to pass through and inhibits the passage of anions. Therefore, the transport number of lithium ions in the cation exchange resin is almost 1. That is, the cation exchange resin is a single ion conductor. On the other hand, in a non-aqueous electrolyte containing a lithium salt, both lithium ions and counter anions move, so the transport number of lithium ions is not 1, and the non-aqueous electrolyte is not a single ion conductor. As described above, since the ion transfer mechanism is different, the interface resistance is large at the interface between the non-aqueous electrolyte and the cation exchange resin layer.
When the cation exchange resin is contained in at least one of the positive electrode and the negative electrode, a lithium conduction path made of the cation exchange resin is formed between the cation exchange resin layer and the positive electrode active material or the negative electrode active material. That is, since lithium ions can move back and forth between the cation exchange resin layer and the positive electrode active material or the negative electrode active material without passing through a non-aqueous electrolyte, the interfacial resistance of the cation exchange resin layer can be reduced. It is presumed that this makes it possible to obtain a non-aqueous electrolyte secondary battery having a high discharge capacity and excellent charge / discharge cycle performance.

The cation exchange resin contained in the positive electrode mixture layer is preferably 10% by mass to 150% by mass with respect to the total mass of the positive electrode mixture layer. When the amount of the cation exchange resin is 10% by mass to 150% by mass with respect to the total mass of the positive electrode mixture layer, continuous lithium ion conduction channels can be formed in the positive electrode mixture layer, which is preferable.

The cation exchange resin contained in the negative electrode mixture layer is preferably 10% by mass to 150% by mass with respect to the total mass of the negative electrode mixture layer. When the amount of the cation exchange resin is 10% by mass to 150% by mass with respect to the total mass of the negative electrode mixture layer, continuous lithium ion conduction channels can be formed in the negative electrode mixture layer, which is preferable.

A positive electrode in which a cation exchange resin is present inside the positive electrode mixture layer can be produced as follows. Particulate positive electrode active material, cation exchange resin, conductive agent, and binder are mixed with a dispersion medium such as alcohol or toluene to prepare a positive electrode mixture paste. The obtained positive electrode mixture paste is applied to both sides of a sheet-shaped positive electrode base material, dried, and then pressed to prepare a positive electrode. As a method of mixing the positive electrode active material, the cation exchange resin, the conductive agent, the binder, etc., for example, a powder mixer such as a V-type mixer, an S-type mixer, a scavenger, a ball mill, or a planetary ball mill The method of mixing by dry or wet is adopted. As the cation exchange resin, the materials mentioned in the first embodiment can be appropriately used.
A negative electrode containing a cation exchange resin inside the negative electrode mixture layer can also be produced by the above method.

By applying the solution containing the cation exchange resin on the positive electrode mixture layer or the negative electrode mixture layer, the cation exchange resin may cover the surface of the positive electrode or the negative electrode. At that time, it is preferable that the cation exchange resin is present on the surface and inside of the mixture layer by allowing the solution containing the cation exchange resin to permeate into the inside of the mixture layer. Examples of the method for applying the solution containing the cation exchange resin include a spray method, a dispense method, a dipping method, and a blade coating method.

The cation exchange resin may be contained in at least one of the positive electrode and the negative electrode, but is preferably contained in the positive electrode and may be contained in both the positive electrode and the negative electrode. Since the cation exchange resin is contained in the positive electrode, the lithium polysulfide generated in the positive electrode during the charge / discharge reaction is suppressed from being eluted into the positive electrode electrolyte existing in the vicinity of the positive electrode, and the capacity of the positive electrode is unlikely to decrease. .. Since the cation exchange resin is contained in the positive electrode and the negative electrode, a lithium ion conduction path is formed by the cation exchange resin from the positive electrode to the negative electrode through the cation exchange resin layer, so that lithium ion conduction is improved. High discharge capacity and charge / discharge efficiency can be achieved.

The non-aqueous electrolyte (positive electrode electrolyte and negative electrode electrolyte) may contain an anion derived from an electrolyte salt. The anion in the present embodiment refers to an anion derived from an electrolyte salt dissolved in a non-aqueous solvent, and an anionic functional group such as a sulfonic acid group contained in the molecular structure of the cation exchange resin, or lithium polysulfide. It does not contain compounds in which some of the sulfides and lithium polysulfides are dissociated and become anionic.
The upper limit of the concentration of the anion contained in at least one of the positive electrode electrolyte and the negative electrode electrolyte is preferably 0.7 mol / l, more preferably 0.5 mol / l, and even more preferably 0.3 mol / l. The upper limit of the concentration of the anion contained in the positive electrode electrolyte is preferably 0.3 mol / l, more preferably 0.2 mol / l, and may be 0 mol / l. When the anion concentration is not more than the above upper limit, the viscosity of the non-aqueous electrolyte can be lowered, and a non-aqueous electrolyte secondary battery having a high discharge capacity and excellent charge / discharge cycle performance can be obtained.

The lower limit of the concentration of the anion contained in at least one of the positive electrode electrolyte and the negative electrode electrolyte may be 0 mol / l, but 0.1 mol / l is preferable, and 0.3 mol / l is more preferable. Excellent charge / discharge cycle performance can be obtained by containing a small amount of anions in the non-aqueous electrolyte.

The positive electrode according to the present embodiment includes a positive electrode base material and a positive electrode mixture layer arranged directly or via an intermediate layer on the positive electrode base material.

As the positive electrode base material, a known material can be appropriately used as long as it is an electronic conductor that does not adversely affect the inside of the battery. Examples of the positive electrode base material include aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc., as well as aluminum and copper for the purpose of improving adhesiveness, conductivity, and oxidation resistance. The surface of which is treated with carbon, nickel, titanium, silver or the like can be used. As the shape of the positive electrode base material, in addition to the foil shape, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foam body, a fiber group forming body and the like are used. The thickness is not particularly limited, but one having a thickness of 1 to 500 μm is used.

The intermediate layer is a coating layer on the surface of the positive electrode base material, and the contact resistance between the positive electrode base material and the positive electrode mixture layer is reduced by containing a conductive agent such as carbon particles. The composition of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a binder and a conductive agent.

The positive electrode mixture layer contains an active material, a conductive agent and a binder, and the active material contains sulfur. As the active material, it is preferable to use sulfur compounded with a conductive material. Examples of the conductive substance include carbon materials such as porous carbon, carbon black, graphite and carbon fiber, and electron conductive polymers such as polyaniline, polythiophene, polyacetylene and polypyrrole. The positive electrode mixture layer may contain an active material other than sulfur, a thickener, a filler and the like, if necessary.
The positive electrode mixture layer may not contain sulfur in a solid state. In this case, the positive electrode mixture layer contains only a conductive agent and a binder, and the lithium polysulfide in the positive electrode electrolyte contributes to charging and discharging as an active material. The inclusion of solid sulfur is preferable because it can improve the discharge capacity and energy density of the non-aqueous electrolyte secondary battery.

As the positive electrode active material other than sulfur, a known material can be appropriately used as long as it is a positive electrode active material that can occlude and release lithium ions. For example, a composite oxide represented by Li _x MO _y (M represents at least one transition metal) (Li _x CoO ₂ , Li _x NiO ₂ , Li _x Mn ₂ O ₄ , Li _x MnO ₃ , Li _x Ni). _y Co _(1-y) O ₂ , Li _x N _y Mn _z Co _(1-y-z) O ₂ , Li _x N _y Mn _(2-y) O ₄ etc.), or Li _w Me _x (XO) _y ) _z (Me represents at least one kind of transition metal, X represents, for example, P, Si, B, V) polyanion compounds (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO) ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F, etc.) can be selected. In addition, the elements or polyanions in these compounds may be partially substituted with other elements or anion species, and the surface is coated with metal oxides such as ZrO ₂ , MgO, Al ₂ O ₃ and carbon. May be good. Further, conductive polymer compounds such as disulfide, polypyrrole, polyaniline, polyparastyrene, polyacetylene, and polyacene-based materials, pseudo-graphite structural carbonaceous materials, elemental sulfur and the like can be mentioned, but are not limited thereto. In addition, these compounds may be used alone or in combination of two or more.

The conductive agent is not limited as long as it is an electronically conductive material that does not adversely affect the battery performance, but for example, natural graphite (scaly graphite, scaly graphite, arsenic graphite, etc.), artificial graphite, carbon black, acetylene black, etc. It is possible to use one or a mixture of two or more conductive materials such as Ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material. it can. Among these, acetylene black is preferable as the conductive agent from the viewpoint of electron conductivity and coatability. The amount of the conductive agent added is preferably 0.1% by mass to 50% by mass, more preferably 0.5% by mass to 30% by mass, based on the total mass of the positive electrode mixture layer. It is preferable to use acetylene black pulverized into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced.

As the binder, a binder generally used for non-aqueous electrolyte secondary batteries can be used, and for example, a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, etc. One or a mixture of two or more polymers having rubber elasticity such as ethylene-propylene-dienter polymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), and fluororubber can be used. The amount of the binder added is preferably 1 to 50% by mass, more preferably 2 to 30% by mass, based on the total mass of the positive electrode mixture layer.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium, it is preferable to inactivate this functional group by methylation or the like in advance.

The filler is not particularly limited as long as it does not adversely affect the battery performance. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

The negative electrode according to the present embodiment includes a negative electrode base material and a negative electrode mixture layer arranged directly on the negative electrode base material or via an intermediate layer. The negative electrode mixture layer contains a negative electrode active material and a binder. The negative electrode mixture layer may contain a conductive agent, a thickener, a filler and the like, if necessary. The intermediate layer of the negative electrode can be the same as the intermediate layer of the positive electrode described above.

The negative electrode active material used in the negative electrode mixture layer is not particularly limited as long as it is a substance that can electrochemically occlude and release lithium ions, and a known material can be used as appropriate. Examples thereof include carbonic materials, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alloys such as lithium alone and lithium aluminum alloys, and metals capable of forming alloys with lithium such as Sn and Si. Examples of the carbonaceous material include graphite (graphite), cokes, non-graphitizable carbon, easily graphitizable carbon, fullerene, carbon nanotubes, carbon black, activated carbon and the like. Among these, graphite is preferable as a negative electrode active material because it has an operating potential extremely close to that of metallic lithium and can be charged and discharged at a high operating voltage. For example, artificial graphite and natural graphite are preferable. In particular, graphite in which the surface of the negative electrode active material particles is modified with amorphous carbon or the like is desirable because it generates less gas during charging. These may be used alone or in any combination and ratio of two or more. Of these, carbonaceous materials or lithium composite oxides are preferably used from the viewpoint of safety.

As the binder used for the negative electrode mixture layer, the above-mentioned various binders can be used. Further, the negative electrode mixture layer may contain the above-mentioned conductive agent, thickener, filler and the like.

As the negative electrode base material, in addition to copper, nickel, iron, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., adhesiveness, conductivity, and reduction resistance For the purpose, one having a surface of copper or the like treated with carbon, nickel, titanium, silver or the like can be used.
As the shape of the negative electrode base material, in addition to the foil shape, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foam body, a fiber group forming body and the like are used. The thickness is not particularly limited, but one having a thickness of 1 to 500 μm is used.

In the present embodiment, the cation exchange resin layer serves as a separator that insulates the positive electrode and the negative electrode. The cation exchange resin layer contains a cation exchange resin. Examples of the cation exchange resin include polyacrylic acid, polymethacrylic acid, polyvinylbenzenesulfonic acid, polybenzenemethanesulfonic acid, and polyacrylamide-2-methyl-1-propanesulfonic acid. Further, a sulfonic acid group to a variety of resin _(-SO 3 H), by introducing a carboxylic acid group (-COOH), or a hydroxyl group (-OH), a can be obtained cation exchange resin. Examples of various resins include perfluorocarbon resin, aromatic polyetherketone resin, polyphenylene sulfide resin, polyethersulfone resin, polyphenylene oxide resin, polybenzimidazole resin and the like.
A perfluorocarbon sulfonic acid resin in which a sulfonic acid group is introduced into a perfluorocarbon resin is preferable because high ionic conductivity can be obtained.

The form in which the cation exchange resin layer contains the cation exchange resin is not particularly limited. A cation exchange membrane formed by forming a cation exchange resin into a film may be used, or a commercially available ion exchange membrane may be used. Specific examples thereof include Nafion membrane (trade name, manufactured by DuPont), Flemion (trade name, manufactured by Asahi Glass), Aciplex (trade name, manufactured by Asahi Kasei) and the like.

The cation exchange resin layer may be formed by filling the inside of the porous structure of the porous layer with the cation exchange resin. The filling method is not particularly limited, and examples thereof include a spray method, a dispense method, a dipping method, and a blade coating method.

The cation exchange resin layer has no pores communicating from one surface to the other, that is, it is non-porous. Due to the non-porous property, the positive electrode electrolyte and the negative electrode electrolyte are not mixed, and the risk of lithium polysulfide reaching the negative electrode is reduced. In addition, at least one surface may have pores or irregularities that do not communicate with the other surface.

Usually, a commercially available cation exchange resin or cation exchange membrane is a proton (H ⁺ ) type in which a proton is bonded to an anionic functional group. When applying a cation exchange resin or a cation exchange membrane to a non-aqueous electrolyte secondary battery, it is preferable to replace the H ⁺ type with a lithium (Li ⁺ ) type. Substitution with Li ⁺ type is performed by immersing the separator in an aqueous solution of lithium hydroxide. After immersion, the separator is washed with deionized water at 25 ° C. until the washing water becomes neutral. The temperature of the lithium hydroxide aqueous solution is preferably 70 ° C. to 90 ° C., and the immersion time is preferably 2 hours to 6 hours.

The cation exchange resin layer preferably contains a non-aqueous solvent for the conduction of lithium ions inside the layer. As the non-aqueous solvent contained in the cation exchange resin layer, various non-aqueous solvents that can be used for the positive electrode electrolyte or the negative electrode electrolyte described later can be appropriately used. The cation exchange resin layer containing no non-aqueous solvent may be applied to the non-aqueous electrolyte secondary battery as it is, but some cation exchange resins have low swellability of the non-aqueous solvent (or non-aqueous electrolyte). Therefore, it is preferable to perform a swelling treatment with a non-aqueous solvent in advance before manufacturing the battery. The swelling treatment is performed by immersing the cation exchange resin layer substituted with the Li ⁺ type in a non-aqueous solvent. The swelling treatment time is preferably 12 to 48 hours.

The amount of the non-aqueous solvent contained in the cation exchange resin layer may be 30% by mass or less with respect to the cation exchange resin layer. With such a configuration, the cation exchange resin layer is appropriately swollen by the non-aqueous solvent, and the movement of lithium ions in the cation exchange resin layer becomes smooth. As a result, the discharge capacity of the non-aqueous electrolyte secondary battery can be increased.

The mass of the non-aqueous solvent contained in the cation exchange resin layer may be adjusted by using a non-aqueous solvent having a low impregnation property in the cation exchange resin, or a non-aqueous solvent in which the cation exchange resin is immersed. The amount of the above may be set to 30% by mass or less with respect to the amount of the cation exchange resin in advance. Examples of the solvent having low impregnation property into the cation exchange resin layer include 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyl diglime, dimethyl ether, and diethyl. Examples thereof include ethers such as ether, chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate. In addition, a non-aqueous solvent used for the positive electrode electrolyte or the negative electrode electrolyte described later can be appropriately used.

Examples of the material constituting the porous layer include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene. Polymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride- Hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer , Vinylidene fluoride-ethylene-tetrafluoroethylene copolymer and the like can be used.

The non-aqueous solvent used for the positive electrode electrolyte and the negative electrode electrolyte is not limited, and those generally proposed for use in lithium secondary batteries and the like can be used. Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, etc. Chain carbonates such as ethyl methyl carbonate; Chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran or its derivatives; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1 , 4-Dibutoxyethane, ethers such as methyl diglime; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sulton or derivatives thereof, etc. alone or a mixture of two or more thereof. These can be mentioned, but are not limited to these.

In the present embodiment, the positive electrode electrolyte or the negative electrode electrolyte may contain an additive. As the additive, an electrolyte additive generally used for a non-aqueous electrolyte secondary battery can be used. For example, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partial hydride of terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, o-cyclohexylfluorobenzene. , P-Cyclohexylfluorobenzene and other partially fluorinated products; fluoroanisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole and 3,5-difluoroanisole. Cyclic carbonates such as vinylene carbonate, methylvinylene carbonate, ethyl vinylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, anhydrous Anhydrous carboxylic acids such as itaconic acid and cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sulton, propensulton, butane sulton, methyl methanesulfonate, busulphan, methyl toluene sulfonate, dimethyl sulfate, ethylene sulfate, sulfolane , Dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylenesulfoxide, diphenylsulfide, thioanisol, diphenyldisulfide, dipyridinium disulfide and other sulfur-containing compounds; perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, titanium Tetraxtrimethylsilylate and the like can be used alone or in admixture of two or more.

As the electrolyte salt contained in the positive electrode electrolyte or the negative electrode electrolyte, a known electrolyte salt can be appropriately used. For example, lithium (Li such as LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN, etc. ), Inorganic ionic salt containing one of sodium (Na) or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO) ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H) ₅ ) ₄ NClo ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NC Lo ₄ , (n-C ₄ H ₉ ) ₄ NI, (C ₂₎ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthate, lithium stearyl sulfonate, lithium octyl sulfonate, lithium dodecylbenzene sulfonate and other organic ionic salts Etc., and these ionic compounds can be used alone or in combination of two or more.

Further, by using a mixture of LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be lowered, so that the temperature is low. It is more preferable because the performance can be improved and self-discharge can be suppressed.

As the non-aqueous electrolyte, a molten salt at room temperature or an ionic liquid may be used.

The non-aqueous electrolyte secondary battery according to the present embodiment is manufactured by the following method. The manufacturing method includes, for example, (1) a step of producing a positive electrode, (2) a step of producing a negative electrode, (3) a step of preparing a positive electrode electrolyte and a negative electrode electrolyte, and (4) a first surface of a cation exchange resin layer. A step of roughening the surface, (5) a step of immersing the cation exchange resin layer in a non-aqueous electrolyte or a non-aqueous solvent, (6) a step of injecting a positive electrode electrolyte between the positive electrode and the cation exchange resin layer, (7). ) A step of injecting a negative electrode electrolyte between the negative electrode and the cation exchange resin layer, (8) The positive electrode and the negative electrode are laminated or wound through the cation exchange resin layer to form an alternately superimposed electrode group. The steps can include (9) a step of accommodating the positive electrode and the negative electrode (electrode group) in the battery container (case), and (10) a step of sealing the opening of the battery container.
The steps (1) to (4) may be performed in any order, and the steps (6) to (8) may be performed simultaneously or sequentially.

Examples of the non-aqueous electrolyte secondary battery of the present embodiment include the non-aqueous electrolyte secondary battery 1 (lithium ion secondary battery) shown in FIG.

As shown in FIG. 1, the non-aqueous electrolyte secondary battery 1 includes a container 3, a positive electrode terminal 4, and a negative electrode terminal 5, and the container 3 is a container body and an upper wall for accommodating an electrode group 2 and the like. It has a lid plate. Further, an electrode group 2, a positive electrode lead 4', and a negative electrode lead 5'are arranged inside the container body.

The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4', and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5'. Although the positive electrode is impregnated with the positive electrode electrolyte and the negative electrode is impregnated with the negative electrode electrolyte, the illustration of the liquid is omitted.

The electrode group 2 includes a positive electrode, a negative electrode, and a separator, and can store electricity. Specifically, as shown in FIG. 2, the electrode group 2 is formed so as to be arranged in layers so that the separator 25 is sandwiched between the negative electrode 23 and the positive electrode 21.

A local schematic cross-sectional view of the electrode group 2 is shown in FIG. The electrode group 2 includes a positive electrode electrolyte 22 between the positive electrode 21 and the separator 25, and a negative electrode electrolyte 24 between the negative electrode 23 and the separator 25. The positive electrode electrolyte 22 and the negative electrode electrolyte 24 may be the same or different. The separator 25 includes a cation exchange resin layer 25a having a first surface 25c and a second surface 25d and a porous layer 25b, and the first surface 25c and the porous layer 25b are in contact with each other. The roughness factor of the first surface 25c of the cation exchange resin layer 25a is 3 or more.
In FIG. 2, the positive electrode electrolyte 22 is arranged between the positive electrode 21 and the porous layer 25b, and the negative electrode electrolyte 24 is arranged between the negative electrode 23 and the cation exchange resin layer 25a. However, since the positive electrode electrolyte 22 is impregnated in the positive electrode 21 and the porous layer 25b and the negative electrode electrolyte 24 is impregnated in the negative electrode 23, the positive electrode 21 is in contact with the porous layer 25b in a normal battery, and the negative electrode 23 is in contact with the negative electrode 23. It is in contact with the cation exchange resin layer 25a. That is, in the battery, the positive electrode 21, the porous layer 25b, the cation exchange resin layer 25a, and the negative electrode 23 are stacked and arranged in this order.

The separator 25 has a structure in which a cation exchange resin layer 25a having a first surface 25c and a porous layer 25b are laminated. The first surface 25c is in contact with the porous layer 25b. The cation exchange resin layer 25a contains a cation exchange resin and suppresses the lithium polysulfide Li ₂ S _x (4 ≦ x ≦ 8) generated in the positive electrode 21 and / or contained in the positive electrode electrolyte 22 from reaching the negative electrode. To do. Therefore, the lithium polysulfide produced at the positive electrode 21 and / or contained in the positive electrode electrolyte 22 is prevented from reaching the negative electrode, and the shuttle phenomenon is suppressed.

In FIG. 2 and the examples described later, the positive electrode, the porous layer, the cation exchange resin layer and the negative electrode are arranged in this order, and the roughness factor of the surface in contact with the porous layer, which is the first surface of the cation exchange resin layer. Is 3 or more, but the roughness factor of the surface in contact with the negative electrode, which is the second surface, may also be 3 or more. That is, the roughness factors of the first surface and the second surface of the cation exchange resin layer may be 3 or more, respectively. By setting the roughness factors on both sides of the cation exchange resin layer to 3 or more, the interfacial resistance of the cation exchange resin layer can be lowered, and the high rate discharge performance of the battery can be improved.

The positive electrode, the cation exchange resin layer, the porous layer, and the negative electrode may be arranged in this order, and the roughness factor of the surface of the cation exchange resin layer in contact with the porous layer may be 3 or more. As a result, the interfacial resistance between the cation exchange resin layer and the porous layer can be reduced. Further, the positive electrode, the porous layer, the cation exchange resin layer, the porous layer, and the negative electrode may be arranged in this order. In this case, it is preferable that the roughness factors on both sides of the cation exchange resin layer are 3 or more. As a result, the interfacial resistance between the cation exchange resin layer and the porous layer can be made low, and the high rate discharge performance of the battery can be improved.

In FIG. 2 and the examples described later, the cation exchange resin layer and the porous layer are each made into one layer, but a plurality of cation exchange resin layers or porous layers may be provided. In this case, the first surface having a roughness factor of 3 or more may be provided on all the cation exchange resin layers, but may be provided on at least one cation exchange resin layer. This is because the interfacial resistance of the cation exchange resin layer can be made low and the high rate discharge performance of the battery can be improved.

The configuration of the non-aqueous electrolyte secondary battery according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery. A power storage device including a plurality of the above-mentioned non-aqueous electrolyte secondary batteries may be used. An embodiment of the power storage device is shown in FIG. In FIG. 3, the power storage device 100 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of non-aqueous electrolyte secondary batteries 1. The power storage device 100 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

(Example 1-1)
As a cation exchange membrane, both sides of a Nafion membrane (manufactured by Sigma Aldrich) having a thickness of 50 μm are coarsely coated with sandpaper No. P320 having a particle size of a polishing material for abrasive cloth specified in JIS R 6010: 2000 of 320 μm. Surfaced. The number of times of polishing with sandpaper was 80 times per side. This membrane is used as the cation exchange membrane of Example 1-1.

(Example 1-2)
The surface of the naphthion membrane was roughened in the same manner as in Example 1-1 except that P400 sandpaper was used. This membrane is used as the cation exchange membrane of Example 1-2.

(Example 1-3)
The surface of the Nafion membrane was roughened in the same manner as in Example 1-1 except that P1000 sandpaper was used. This membrane is used as the cation exchange membrane of Example 1-3.

(Examples 1-4) to (Examples 1-6)
Examples 1-4 in the same manner as in Examples 1-3, except that the number of times of polishing with sandpaper was changed and the roughness factor, arithmetic mean roughness Ra, and maximum height roughness Rz were set to the values shown in Table 1. A cation exchange membrane of ~ 1-6 was prepared.

(Comparative Example 1-1)
The naphthion membrane that has not been roughened is used as the cation exchange membrane of Comparative Example 1-1.

[1. Surface morphology observation]
Under the following conditions, the surface morphology of the cation exchange membranes of Examples 1-1 to 1-6 and Comparative Example 1-1 was observed, and the roughness factor, the arithmetic mean roughness Ra, and the maximum height roughness Rz were calculated. did.
-Measuring equipment: Ultra-depth shape measuring microscope VK-8500 (manufactured by KEYENCE)
-Measurement range: 1.04 x 10 ^-3 cm ²
-Shape analysis application: VK-H1A9 (manufactured by KEYENCE)

[2. Interface resistance measurement]
[2-1. Impregnation treatment of cation exchange membrane]
The cation exchange membranes of Examples 1-1 to 1-6 and Comparative Example 1-1 are immersed in a 1 mol / l lithium hydroxide water / alcohol solution and stirred at 80 ° C. for 12 hours to exchange cations. The protons in the membrane were exchanged for lithium ions. The cation exchange membranes of each Example and Comparative Example after stirring were washed with deionized water and dried under degassing at 120 ° C. to remove lithium hydroxide and a solvent.
The obtained Li ⁺ type cation exchange membrane was mixed with 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) at a volume ratio of 50:50 in a mixed solvent at 25 ° C. for 12 hours. The impregnation treatment was performed by immersing. By this treatment, the cation exchange membrane after the impregnation treatment was impregnated with a mixed solvent in an amount of 20% by mass based on the mass of the cation exchange membrane before the impregnation treatment. The thickness of the cation exchange membrane before and after the impregnation treatment was 50 μm and 64 μm, respectively.

[2-2. Measurement of electrolyte layer resistance R]
A resistance measurement cell 30 was prepared using the cation exchange membranes of the examples and comparative examples after the impregnation treatment and the electrochemical measurement cell 31 (manufactured by Tomcell Japan) as shown in FIG. A stainless steel plate electrode 31e and a porous film (porous layer) 36 sandwich a cation exchange resin layer 35 inside an O-ring 31f having an inner diameter of 26 mm and an outer diameter of 34 mm provided on a stainless steel plate support 31a. Laminated with. The resistance measurement cell 30 was assembled by stacking the stainless steel plate lid 31b on the laminated body and fastening the bolt 31c and the nut 31d. The polyethylene microporous membrane 36 contains 0.3 mol / l lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), and contains a non-aqueous electrolyte in which DME and DOL are mixed at a ratio of 50:50 (volume ratio). It is impregnated.

The electrolyte layer resistance R was measured by AC impedance measurement using the resistance measurement cell. The AC impedance measurement was performed at an applied voltage amplitude of 5 mV and a frequency of 1 MHz to 100 MHz. A Nyquist diagram of the measurement results was prepared and fitted using an equivalent circuit. Of the intersections of the curve fitted with the arc that appears on the highest frequency side and the actual axis, the value on the low frequency side was read and used as the electrolyte resistance R. The electrolyte layer resistance R is the porous layer resistance Re, which is the resistance of the polyethylene microporous membrane 36, the interface resistance Ri, which is the interface resistance between the polyethylene microporous membrane 36 and the cation exchange membrane 35 after the impregnation treatment, and the impregnation treatment. The cation exchange resin layer resistance Rc, which is the resistance of the cation exchange membrane 35 later, is included and is represented by the following formula (1).
R = 2Re + 2Ri + Rc (1)

[2-3. Measurement of cation exchange resin layer resistance Rc]
Except for the absence of a polyethylene microporous membrane impregnated with an electrolytic solution containing DME: DOL = 50: 50 (volume ratio) containing 0.3 mol / l LiTFSI [2-2. The AC impedance was measured in the same manner as in the measurement of the electrolyte layer resistance R]. The resistance obtained by this measurement was defined as the cation exchange resin layer resistance Rc.

[2-4. Measurement of porous layer resistance Re]
Without arranging the cation exchange membrane after the impregnation treatment, only one polyethylene microporous membrane impregnated with the electrolytic solution containing DME: DOL = 50: 50 (volume ratio) containing 0.3 mol / l LiTFSI was arranged. Other than what you did [2-3. Measurement of cation exchange resin layer resistance Rc], AC impedance measurement was performed. The resistance obtained by this measurement was defined as the porous layer resistance Re.

The interface resistance Ri was calculated using the formula (1) from the values of the electrolyte layer resistance R, the cation exchange resin layer resistance Rc, and the porous layer resistance Re obtained by the AC impedance measurement.

The concentration of LiTFSI in the electrolytic solution impregnated in the polyethylene microporous membrane was changed to the value shown in Table 2, and the AC impedance was measured using the cation exchange membranes of each Example and Comparative Example after the impregnation treatment, and the interface was measured. The resistance Ri was calculated. When the concentration of LiTFSI was 0.5 mol / l, only Examples 1-1 to 1-3 and Comparative Example 1-1 were measured.

Using the cation exchange membranes of Examples 1-2 and Comparative Example 1-1, the sulfur conversion concentration of lithium polysulfide in the electrolytic solution impregnated in the polyethylene microporous membrane was set to 3.0 mol / l, and the concentration of LiTFSI was adjusted. After changing to the values shown in Table 3, the AC impedance was measured and the interfacial resistance Ri was calculated.
The electrolytic solution containing lithium polysulfide was prepared as follows. In a glove box with a dew point of -50 ° C or lower, lithium polysulfide (Li ₂ S) and sulfur (S ₈ ) are combined with DME in a stoichiometric ratio (molar ratio 8: 5) that Li ₂ S ₆ can produce. DOL was put into a non-aqueous solvent mixed at a volume ratio of 50:50, and the mixture was stirred. This solution was sealed in a closed container and allowed to stand in a constant temperature bath at 80 ° C. for 4 days to react Li ₂ S and S ₈ to prepare a solution containing lithium polysulfide. In this lithium polysulfide solution, lithium polysulfide corresponding to 3.0 mol / l in terms of sulfur is dissolved. LiTFSI was dissolved in this solution so that the concentration of LiTFSI was 0, 0.3, 0.5 or 1.0 mol / l to prepare an electrolytic solution containing lithium polysulfide.

Table 1 shows the roughness factor, arithmetic mean roughness Ra, and maximum height roughness Rz of the cation exchange membranes of each example and comparative example, and the concentrations of the cation exchange membrane after impregnation treatment, LiTFSI, and lithium polysulfide were changed. Tables 2 and 3 show the interfacial resistance Ri with the polyethylene microporous membrane containing the electrolytic solution at that time. A graph obtained by plotting the value obtained by dividing the interfacial resistance of Examples 1-1 to 1-6 by the interfacial resistance of Comparative Example 1-1 with respect to the roughness factor, the arithmetic mean roughness Ra, and the maximum height roughness Rz. It is shown in 6-8.

As shown in Table 1, it was found that the roughness factor, the arithmetic mean roughness Ra, and the maximum height roughness Rz were all increased by performing the roughening treatment with sandpaper. Further, as shown in Tables 2, 3 and 4 to 6, the cation exchange of Examples 1-1 to 1-6 in which the roughening treatment was performed was performed regardless of the concentration of LiTFSI or the presence or absence of lithium polysulfide. It was clarified that the interfacial resistance Ri of the film was reduced as compared with the cation exchange membrane of Comparative Example 1-1 which had not been roughened. Further, in Examples 1-1 to 1-4 in which the maximum height roughness of the surface of the cation exchange membrane is 10 μm or more when the concentration of LiTFSI is as low as 0.3 mol / l, the maximum height roughness is 10 μm. It was found that the interfacial resistance was lower than that of Examples 1-5 and 1-6, which were less than. Further, when the concentration of LiTFSI is as high as 1.0 mol / l, Examples 1-1 to 1-3 and Examples 1-5 and 1-6 having an arithmetic mean roughness Ra of 0.5 μm or more are It showed lower interfacial resistance as compared with Examples 1-4 in which the arithmetic mean roughness Ra was less than 0.5 μm.
As shown in Table 3, it was found that the interfacial resistance is reduced by roughening the surface of the cation exchange membrane even when lithium polysulfide is contained.

[3. High rate discharge test]
(Example 2-1)
Magnesium citrate was carbonized at 900 ° C. in an argon atmosphere for 1 hour, and then immersed in a 1 mol / l sulfuric acid aqueous solution to extract MgO. Subsequently, it was washed and dried to obtain porous carbon. The porous carbon and sulfur were mixed at a mass ratio of 30:70. This mixture was sealed in a closed container under an argon atmosphere, heated to 150 ° C. at a heating rate of 5 ° C./min, held for 5 hours, and then allowed to cool to 80 ° C. Then, the temperature was raised again to 300 ° C. at a heating rate of 5 ° C./min and heat treatment was performed to hold the temperature for 2 hours to obtain a carbon-sulfur composite (hereinafter, also referred to as “SPC composite”).

A positive electrode paste containing SPC composite as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder at a mass ratio of 85: 5:10, and N-methylpyrrolidone (NMP) as a solvent. Was produced. The obtained positive electrode paste was filled in a nickel mesh current collector and then dried to prepare a positive electrode plate. The amount of the positive electrode paste applied was 1.2 mg / cm ² .

As the negative electrode plate, a copper foil having a thickness of 10 μm was attached with metal Li to make the entire negative electrode thickness 310 μm.

As the cation exchange membrane, a P400 sandpaper was used, and a Nafion membrane obtained by roughening only one side was used.

As the positive electrode electrolytic solution, a solution containing lithium polysulfide at a sulfur equivalent concentration of 3.0 mol / l and mixing DME and DOL at a volume ratio of 50:50 was used.

As the negative electrode electrolyte, a solvent in which DME and DOL were mixed at a volume ratio of 50:50 was used.

A test cell 40 was produced using an electrochemical measurement cell 41 (manufactured by Tomcell Japan, Inc.) as shown in FIG. First, the positive electrode 43 produced as described above is arranged inside the O-ring 41f having an inner diameter of 26 mm and an outer diameter of 34 mm provided on the stainless steel plate support 41a. After laminating the porous film (porous layer) 46 impregnated with the positive electrode electrolyte, the cation exchange resin layer 45 having a size larger than the inner diameter of the O-ring was arranged. At this time, the cation exchange resin layer 45 was arranged so that the first surface 45a subjected to the roughening treatment was in contact with the porous film 46. A negative electrode 44 impregnated with a negative electrode electrolyte was laminated on the negative electrode 44. The test cell 40 (hereinafter, also referred to as “battery”) is formed by arranging the stainless steel plate electrode 41e on the negative electrode 44, overlapping the stainless steel plate lid 41b, and fastening the bolt 41c and the nut 41d. Assembled. This is referred to as Example Battery 2-1.

(Comparative Example 2-1)
A test cell 30 according to Comparative Example 2-1 was prepared in the same manner as in Example 2-1 except that a Nafion membrane which had not been roughened was used as the cation exchange membrane. This is referred to as Comparative Example Battery 2-1.

The 0.1C discharge capacity and the 0.2C discharge capacity of the Example battery 2-1 and the Comparative Example battery 2-1 are measured by the following method, and the 0.2C discharge capacity is divided by the 0.1C discharge capacity. The 0.2C / 0.1C ratio (%) was calculated.
0.1C constant current discharge up to 1.5V and 0.1C constant current charge up to 3.0V were performed at 25 ° C. The charging and discharging termination conditions were set until the set voltage was reached or 10 hours had passed. This cycle was repeated 3 cycles, with the process of discharging and charging 0.1C as one cycle. The value obtained by dividing the discharge capacity in the third cycle by the mass of the SPC composite was defined as 0.1C discharge capacity (mAh / g).
In 1C, when the capacity per mass of the SPC composite used as the positive electrode active material was set to the theoretical capacity of 1675 mAh / g, the capacity of the positive electrode active material was set to the current value for discharging in 1 hour.
Next, 0.2C constant current discharge up to 1.5V and 0.2C constant current charge up to 3.0V were performed at 25 ° C. The charging and discharging termination conditions were set until the set voltage was reached or 5 hours had passed. This cycle was repeated 3 cycles, with the process of discharging and charging 0.2C as one cycle. The value obtained by dividing the discharge capacity in the third cycle by the mass of the SPC composite was defined as 0.2C discharge capacity (mAh / g). The 0.2C / 0.1C ratio (%) was calculated by dividing the 0.2C discharge capacity by the 0.1C discharge capacity.

Table 4 shows the 0.1C discharge capacity, the 0.2C discharge capacity, and the 0.2C / 0.1C ratio (%) of the Example Battery 2-1 and the Comparative Example Battery 2-1. Further, the discharge curves of 0.1C and 0.2C of the example battery 2-1 and the comparative example battery 2-1 are shown in FIG.

The battery 2-1 of Example showed a high discharge capacity of 1150 mAh / g at both 0.1C and 0.2C discharge currents, and the 0.2C / 0.1C ratio was 100%. On the other hand, the comparative example battery 2-1 had a 0.1C discharge capacity equivalent to that of the example battery 2-1 but a low 0.2C discharge capacity and a 0.2C / 0.1C ratio of 71.7. %Met. It is considered that this is because in the battery 2-1 example, since the cation exchange membrane whose surface was roughened was used as the cation exchange resin layer, the interfacial resistance was lowered and the high rate discharge performance was improved.
In the battery 2-1 of the example, as shown in FIG. 9A, the discharge potential did not decrease even after 1150 mAh / g discharge corresponding to the capacity of sulfur in the positive electrode active material layer. On the other hand, in Comparative Example Battery 2-1 as shown in FIG. 9B, a phenomenon in which the discharge potential decreased at the end of discharge was observed. It is considered that this is because the interfacial resistance of the cation exchange resin layer was lowered by the roughening treatment, and the current distribution on the positive electrode surface became more uniform. In addition, the roughening treatment improved the retention of lithium polysulfide on the surface of the positive electrode, which increased the contribution of lithium polysulfide contained in the positive electrode electrolyte to the charge / discharge reaction. it is conceivable that.

According to this embodiment, since a non-aqueous electrolyte secondary battery having excellent high rate discharge performance can be obtained, it is useful as a secondary battery for a wide range of applications such as in-vehicle use and stationary use.

1 Non-aqueous electrolyte secondary battery 2 Electrode group 3 Battery container 4 Positive electrode terminal 4'Positive lead 5 Negative terminal 5'Negative lead 20 Power storage unit 21, 43 Positive electrode 22 Positive electrode electrolyte 23, 44 Negative electrode 24 Negative electrolyte 25 Separator 25a, 35, 45 Cationic exchange resin layer 25b, 36, 46 Porous layer (porous film)
25c, 45a First surface 25d Second surface 30 Resistance measurement cell 31, 41 Electrochemical measurement cell 31a, 41a Support 31b, 41b Lid 31c, 41c Bolt 31d, 41d Nut 31e, 41e Electrode 31f, 41f O- Ring 40 Test cell 100 Power storage device

Claims (12)

With a positive electrode containing sulfur,
With the negative electrode
With non-aqueous electrolyte
A non-aqueous electrolyte secondary battery comprising a cation exchange resin layer arranged between a positive electrode and a negative electrode and having a first surface having a roughness factor of 3 m ² / m ² or more. The non-aqueous electrolyte secondary battery according to claim 1, wherein the arithmetic average roughness Ra of the first surface of the cation exchange resin layer is 0.5 μm or more. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the maximum height roughness Rz of the first surface of the cation exchange resin layer is 5 μm or more. Further, a porous layer is provided, and the porous layer is in contact with the first surface of the cation exchange resin layer.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3. The non-aqueous electrolyte includes a positive electrode electrolyte and a negative electrode electrolyte.
Positive electrode electrolyte contains lithium polysulfide
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the sulfur equivalent concentration of the positive electrode electrolyte is higher than the sulfur equivalent concentration of the negative electrode electrolyte. The non-aqueous electrolyte secondary battery according to claim 5, wherein the sulfur equivalent concentration of the positive electrode electrolyte is 1.2 mol / l or more. The non-aqueous electrolyte secondary battery according to claim 6, wherein the sulfur equivalent concentration of the positive electrode electrolyte is 3.0 mol / l or more. The non-aqueous electrolyte secondary battery according to any one of claims 5 to 7, wherein the sulfur equivalent concentration of the positive electrode electrolyte is 18 mol / l or less. The non-aqueous electrolyte secondary battery according to any one of claims 5 to 8, wherein the concentration of anions contained in at least one of the positive electrode electrolyte and the negative electrode electrolyte is 0.7 mol / l or less. The non-aqueous electrolyte secondary battery according to any one of claims 5 to 9, wherein the concentration of the anion contained in the positive electrode electrolyte is 0.3 mol / l or less. At least one of the positive electrode and the negative electrode is provided with a cation exchange resin,
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the concentration of anions contained in the non-aqueous electrolyte is 0.7 mol / l or less. A method for manufacturing a non-aqueous electrolyte secondary battery, which comprises a positive electrode containing sulfur, a negative electrode, and a cation exchange resin layer having a first surface having a roughness factor of 3 or more, which is interposed between the positive electrode and the negative electrode. ,
A positive electrode containing lithium polysulfide is injected between the positive electrode and the cation exchange resin layer, and a negative electrode having a lower concentration of lithium polysulfide than the positive electrode is injected between the negative electrode and the cation exchange resin layer. A method of manufacturing a non-aqueous electrolyte secondary battery, including

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